This invention relates to a high pressure fuel injector unit for an engine and more particularly to an improved injection unit and method of operating it to insure that there will be good performance under all speed conditions without knocking or other objectionable engine characteristics and good exhaust control.
The use of fuel injectors to improve engine combustion is well known. A fuel injector generally employs a more accurate fuel control and hence will accommodate better engine performance including greater power, better fuel economy, and improved exhaust emission control. One popular type of fuel injector is the so-called "accumulator type". With this type of injector, fuel is supplied under pressure to an accumulator chamber and an injection valve is opened and closed in order to discharge fuel under pressure from the accumulator chamber into the engine. The injection valve is opened and closed by varying the pressure within a control chamber which control chamber receives fuel under pressure from the accumulator chamber.
Despite the advantages of the accumulator type fuel injector, there still can be some problems in providing adequate fuel and the appropriate timing therefore under all running conditions. This is particularly true when the injector is used in conjunction with an engine operating on the diesel cycle.
The control chamber is normally depressurized by opening a control valve that is solenoid operated and hence the opening and closing of the injector valve is related to the energization of the solenoid. Obviously, the amount of fuel injected will determine the speed and load capabilities of the engine. Normally, the speed of the engine increases or the load or power output of the engine increases as the amount of fuel injected increases. However, if the amount of fuel discharged is controlled solely by controlling the duty cycle of the solenoid, certain problems can occur. This is because of the fact that if injection is started too early in the cycle, there is a likelihood of pre-ignition or knocking and also excess NOX emissions. If, however, the injections carries over too long after top dead center, HC and CO emissions will be present in the exhaust gases and fuel comsumption can rise abruptly.
If the amount of fuel is controlled solely by the duty cycle, than a high accumulator pressure is required to insure that all fuel necessary for high performance can be injected into the engine without causing the aforenoted deleterious affects of too early and too late injection. On the other hand, such high pressure gives rises to further problems when the engine operates at low speeds since the duty cycle becomes extremely short and optimum timing is also not possible.
It is, therefore, a principal object of this invention to provide an improved accumulator type fuel injector and method of operating it.
It is another object to this invention to provide an improved arrangement for controlling the speed and output of an injected engine without causing undo emissions of NOX, HC or CO, or knocking, or poor fuel economy.